This invention relates, in an electromagnetic data-storage (information storage and retrieval) system, to the contact (communication) interface between the recording surface of a rigid information storage magnetic recording medium (device), such as a disk, and a read/write head (or transducer) structure which operates in substantially continuous dynamic contact with the medium""s surface during reading and writing operations. In particular, the invention focuses upon both the structural characteristics of such a contact interface, and upon the process and methodology of preparing and creating that interface. From another point of view, the invention disclosed herein also relates to a contact recording electromagnetic information storage and retrieval system, also called a read/write system, wherein several important features interact. This system includes, inter alia, a rigid magnetic recording medium, or device, having a surface associated with an adjacent information storage layer, an elongate flexure, a transducer portion joined to, and carried/supported/biased by, that flexure including read/write pole structure embedded within a circumsurrounding, medium-contacting wear pad, and a contact interface in the region of contact between the transducer/wear pad/medium surface which meets the criteria of other features of the present invention. This invention also pertains to the surface structure, per se, of a rigid recording medium.
The term xe2x80x9crecording surfacexe2x80x9d is employed herein as a verbal artifact, widely recognized in the art, to refer collectively to a solid-material structure, typically a layered structure, including the usual information-storage magnetic-recording-layer substructure (typically one or two layers), and the normal protective overcoat (if any) provided on the xe2x80x9ctransducer sidexe2x80x9d of the magnetic-recording-layer substructure.
While, to the naked eye, the recording surface of a modern rigid recording medium, such as a rigid disk, appears to be absolutely flat and smooth, on a microscopic level, such a surface is, in truth, inherently irregular, to different degrees of irregularity depending upon the associated surface-preparation technique(s). As will become very apparent from the explanatory and descriptive material which follows hereinbelow, our creation and development of the present invention has involved, largely, an exploration of the microscopic surface irregularity in such a setting. Given this situation, we view the interface surface structure discussed and claimed hereinxe2x80x94the landscape, so to speakxe2x80x94in terms of topography and peaks and valleys, etc.
As has just been expressed above in the xe2x80x9cField of the Inventionxe2x80x9d section, the novel system, medium and interface of the present invention, and the associated creational processing and methodology, exist in relation to, and in the regime of, contact recording, and in the context of a contact recording system including other important interactive and cooperative structural elements and features. This is a regime which represents a substantial departure from the conventional art of the standard xe2x80x9cflyingxe2x80x9d, take-off-and-landing-type systemsxe2x80x94a departure which has been pioneered and led by the Censtor Corporation of San Jose, Calif.
While the contributions of the present invention clearly offer utility in a variety of rigid-medium systems, we describe and illustrate those contributions herein particularly in the setting of rigid-disk recordingxe2x80x94a setting wherein the invention has been found to proffer great immediate commercial promise.
Most of the pioneering and significant work in this field is disclosed and illustrated in the following, listed U.S. patents and pending U.S. patent applications, and it is our intent, as is now expressed, to have the full disclosure contents of each and every one of these listed patents and patent applications fully incorporated herein by reference:
(a) U.S. Pat. No. 4,751,598, issued Jun. 14, 1988;
(b) U.S. Pat. No. 4,860,139, issued Aug. 22, 1989;
(c) U.S. Pat. No. 5,041,932, issued Aug. 20, 1991;
(d) U.S. Pat. No. 5,073,242, issued Dec. 17, 1991;
(e) U.S. Pat. No. 5,111,351, issued May 5, 1992;
(f) U.S. Pat. No. 5,163,218, issued Nov. 17, 1992;
(g) U.S. Pat. No. 5,174,012, issued Dec. 29, 1992;
(h) U.S. Pat. No. 5,063,712, issued Nov. 12, 1991;
(i) U.S. Pat. No. 4,757,402, issued Jul. 12, 1988;
(j) U.S. Pat. No. 4,636,894, issued Jan. 13, 1987;
(k) U.S. Pat. No. 4,423,450, issued Dec. 27, 1983;
(l) U.S. patent application Ser. No. 08/191,967, filed Feb. 4, 1994;
(m) U.S. patent application Ser. No. 07/992,886, filed Dec. 14, 1992;
(n) U.S. patent application Ser. No. 07/990,005, filed Dec. 10, 1992;
(o) U.S. patent application Ser. No. 07/989,170, filed Dec. 10, 1992;
(p) U.S. patent application Ser. No. 07/806,577, filed Dec. 21, 1991;
(q) U.S. patent application Ser. No. 07/966,095, filed Oct. 22, 1992;
(r) U.S. patent application Ser. No. 08/011,890, filed Feb. 1, 1993; and
(s) U.S. patent application Ser. No. 08/338,394, filed Nov. 14, 1994.
As is recognized in the leading work done by the Censtor Corporation, contact reading and writing offers the most intimate working relationship between a read/write head and a rigid magnetic recording surface. Such intimacy, for a given head geometry, offers the maximum possible linear recording density and signal output level. However, and focussing illustrative attention hereinafter throughout on rigid disk recording, contact operation introduces, significantly, the issue of wear which takes place within the head/disk interface. And, while wear involves both head wear and media wear, in contact operation, it is head wear that is far the more important issue, and is the key factor which decides the usable lifetime of a given recording system. Accordingly, the primary focus of the work leading to the present invention has been solving the problem of head wear.
Accepting the fact that some wear often occurs wherever there is relative motion between two bodies in contact, the challenge of maintaining head wear within acceptable limits in the setting of contact recording is fundamentally one of tribology. Thus, a functional thrust of the present invention has been to establish a contact, head/disk interface which will lead to a head-wear characteristic, or performance, offering a system having, as an illustration, a usable lifetime of five years, under conditions of continuous (24-hours-per-day, everyday) operation.
In the interface proposed by the present invention, the read/write head is embedded, and exposed in a disk-contacting face, within a tiny-footprint (typically about 20-xcexcm by 20-xcexcm) contact, or wear, pad. In such a setting, pad wear must be less than about 5-xcexcm total height change for most read/write transducers. For wear-pad lateral dimensions of 20-xcexcm by 20-xcexcm mentioned in the illustration above, this corresponds to a volumetric wear rate of less than about 2000-xcexcm3 over the total intended interface lifetime of about 5-years. Such a volume of wear, of course, must be scaled accordingly to accommodate different wear-pad dimensions, as well as to account for the presence of multiple disk-contacting wear pads. The single-pad head geometry tested in one embodiment of the present invention was capable of tolerating the wear volume just mentioned (about 2000-xcexcm3) without degradation of read/write performance.
In point of fact, we have discovered that an interface constructed in accordance with the teachings of this invention can lead to as low a figure as 0.1-xcexcm of vertical wear for over 5-years of continuous-duty operation in a 48-mm disk drive system. When a limited duty cycle of less than 24-hours-per-day is taken into considerationxe2x80x94a duty cycle which typifies the operation of small disk drive systems, head-wear life projections extend far beyond the 5-year satisfactory performance mark.
Preferably, a plurality of the asperities that are within the 100-xcexcm squared area, rise at least 5-nm from an interposed recess within a 10-xcexcm lateral extent.
Another permutation of Specification I is for the surface, in its upper most reaches, to include asperities whose tops have an average radius of curvature in the range of about 2.0-xcexcm to about 100-xcexcm.
The asperities referred to in the definition of Specification I may also be referred to as xe2x80x9cprotrusionsxe2x80x9d and may take the form of curvilinear ridges which are separated by grooves, for example, elongate ridges rising at least 5-nm from interposed grooves extending in non-radial directions.
Similar impressive wear performance is achieved in other-disk-size systems. A 48-mm system has simply been chosen in this and following discussions for the purpose of illustration of the invention.
One feature of the interface of this invention which we believe may play a participating role in minimizing head wear relates to materials. Specifically, our proposed interface is one that exists, with lubricant present, preferably between two amorphous surface materials, such as chemical-vapor-deposited (CVD) carbon, hydrogenated or nonhydrogenated carbon, nitrogenated or nonnitrogenated carbon, silica and others. Indeed, low-wear performance was first noticed in the contact interface present in the systemic structure described in the ""932 patent listed above.
In an embodiment of the invention wherein a single pole-structure-carrying wear pad is rigidly fixed to a suspension, we have devised a wear-rate test with respect to variations in pitch of suspension, the results of which can be used to establish the presence of an interface both made in accordance with the teachings of this invention and capable of sustaining the long period of continuous operation suggested hereinabove as desirable.
Beginning with a flat-lapped pole-structure-carrying wear pad, this test is performed, starting with substantially zero separation (i.e., contact between the pole structure and disk), followed by tilting of the pole-structure-carrying wear pad onto a single edge, applying a known load between this edge and the disk, and reading signal amplitude monitored with respect to written or rewritten data present on the disk. The first-gathered signal-amplitude data, during head/disk contact, tells one the maximum amplitude to be expected. Regarding, then, the test time and data received after tilting of the pad, the appropriate amplitude/separation loss equation is applied to determine the instantaneous head/disk separation as the signal amplitude xe2x80x9cgrows backxe2x80x9d (as the pole structure reapproaches contact with the disk), from which is calculated the volume removed from the pad due to wear. This method is applicable to both single track and full surface sweep wear rate criteria. The method also provides information regarding the change in wear rate as a function of time.
An alternative to the xe2x80x9ctiltxe2x80x9d protocol just described, measures the height of the pole-structure-containing wear pad before and after extended sliding of the wear pad on a disk""s surface, using either fixed or gimbaled heads, and ordinarily operated in the continuous-sweep mode. The volumetric wear may be obtained by converting the pad height measurements to a change in pad volume. Although this method does not provide information regarding any change in wear with time, it does permit wear rates to be measured for interfaces where electrically-functioning read/write transducers are not available.
In tests performed in accordance with these protocols, we have found that the interface created according to the teachings of this disclosure is characterized by a head-wear performance wherein the volume of head-structure wear, over a 12-hour continuous period of fixed-track-mode contact (3600-rpm; linear relative velocity of about 7.5-m/sec) between a linear edge of a head/wear-pad structure and the surface of the associated rigid disk, and under a contact load of about 40-milligrams, is only typically about 0.7-xcexcm3 (and in the range generally of about 0.4- to about 1.0-xcexcm3). Such extraordinarily low wear, after the 12-hour period just mentioned, and with the contacting edge of the head structure beginning as a relatively sharp right-angle edge, is not resolvable by even the most powerful available optical microscopes.
This exceptional head-wear performance data acquired in the xe2x80x9c12-hourxe2x80x9d test, coupled with the observed reduction of wear rate with time, as well as additional data derived from longer-term wear testing, establishes that the requirement of 5-year continuous-operation longevity can predictably be met by our new interface. Systems tested with a contact interface outside the teachings of this invention, for example, have exhibited functional lives as short as 4-6-months, continuous operation.
Accordingly, a general object of the present invention is to provide a contact interface of the type generally described above which is capable of demonstrating the extraordinarily low wear performance just mentioned.
A related object is to provide, on what might be thought of as the xe2x80x9crigid-disksidexe2x80x9d (rigid-medium side) of such a contact interface, a disk recording surface, in either a texturized or an untexturized form, having the appropriate structural, topographical characteristics, particularly with respect to the uppermost part of the surface, which enable achievement of the wear performance mentioned.
A further object of the present invention is to provide, in the setting of such a contact interface, a read/write, pole-structure-bearing contact pad designed to contact-coact with such a disk recording surface to yield operational wear performance at the very low wear levels noted earlier. One can view the contact pad as being wrapped around the pole structure.
An object of the invention which is closely related to the first three objects just stated above, is to provide an electromagnetic disk drive read/write contact system which includes an interface of the type generally mentioned, in a setting where the pole-structure-bearing contact pad forms part of structure that is joined to an elongate slender flexure via which the transducer is positioned adjustably (as, for example, by servo-controlled actuator structure) over the recording surface in a motor-rotated rigid disk.
Another object of the invention is to provide an interface of the type generally set forth, wherein the pole-structure-bearing contact pad includes pole structure exposed in a circumsurrounding surface of amorphous, nanocrystalline, or like wear material, such as chemical-vapor-deposited (CVD), alumina, carbon or silica, with the prepared surface of the disk in the interface designed not only to achieve the remarkably low wear rate mentioned hereinabove, but also designed to minimize, substantially to imperceptibility, differential-wear pole-tip recession (from the contacting surface of the pad) over the expected, normal, useful, working lifetime of the disk, i.e. at least about 5-years.
It is also an object of the invention to provide a unique process and methodology for preparing a contact interface of the type which has just been generally discussed, with particular focus on the preparation of a rigid-disk recording surface having an uppermost surface area with the desired structural, topographical characteristics. Such a process may or may not involve steps for texturizing relatively lower levels of the recording surface. It may also involve retroprocessing of commercially available texturized disks to modify the uppermost topographical features therein.
Yet another object of the present invention is to provide a dual-surface-characteristic rigid recording medium, such a disk, wherein, for example, the recording-surface area is texturized to reduce contact friction, and an adjacent area, preferably near the inner diameter (ID) of a disk, is nontexturized to provide a stationary, enhanced-capillary-adhesion parking-surface area for receiving transducer contacting structure during periods of nonoperation.
In the process of discovering and examining and testing those key features and process constraints which lie at the core of this invention, we have reached the surprising discovery that, essentially regardless of the character of surface topography at lower elevations of a recording surface, it is the topography of the uppermost reaches of that surface, for example the highest 1.0%, which dictates, and differentiates, the regimes, on the one hand of unacceptable, high-wear contact performance, and on the other hand, of dramatically improved and fully acceptable, low-wear contact performance. In essence, we have discovered that one can substantially ignore topographical features below the uppermost reaches of the surface, and achieve surprisingly acceptable wear performance by directing attention only toward establishing topographical features in the highest regions of the landscapexe2x80x94features which come within any one of the several surface-quality Specifications identified and described hereinbelow as Specifications I, II and III. This recognition about the region of most important interest, vis-a-vis controlling wear, opens the door, as we have found, to the creation and successful utilization of this invention with respect to a whole host of different types of disk surfaces, including disk surfaces which have the very smoothest landscapes (nontexturized surfaces), as well as those with the roughest landscapes (texturized surfaces characterized by plural, concentric, alternating, annular grooves and ridges).
While we recognize that the creation of a disk surface having the desirable topographical characteristics may be prepared perhaps in a variety of different ways, we have determined that a very important and very successful technique for achieving final acceptable surface topography involves a buffing procedure which we refer to herein as kiss-buffing (to be described below). We also refer to this procedure as process-grading.
According to a preferred embodiment of the invention, the proposed contact interface takes the form of an organization including a rigid recording disk having a magnetic recording surface with a topography characterized by a defined surface quality which meets any one of three surface-quality Specifications (described below in detail as Specifications I, II and III). A fluorocarbon or hydrocarbon lubricant film, for example, of perfluoropolyether or phosphazene, is distributed on the recording surface with a thickness in the range of about 1- to about 2.5-nm (and preferably no less than about 1-nm) as measured by any one of three techniques (identified and described in detail below as Techniques I, II and III). At least one read/write, pole-structure-bearing contact pad (or instrumentality) is in contact with the lubricated surface. The pole structure is embedded within and circumsurrounded by the pad.
A preferred method of preparing such a contact interface, according to one way of practicing the invention, includes generally, and beginning with a disk blank having a surface which has been coated with a metallic underlayer, (1) polishing the coated surface, (2) washing the polished surface, (3) applying a layer (or layers, where required) of magnetic recording material to the washed surface and overcoating the same with a layer of carbon or silica, (4) kiss-buffing (fully described below) the overcoat, (5) washing the kiss-buffed surface to effect surface debris removal, (6) lubricating (and then wiping excess lubricant from) that washed surface, and (7) conducting a glide-height test. Surface polishing (step (1) above) is accomplished by a unique two-stage (two-step) polishing procedure also described below.
Another method according to the present invention for preparing a recording surface exhibiting the desired wear performance, involves kiss-buffing a previously roughened or texturized surface of a recording medium to reduce asperity height on, and to smooth the tops of, the ridges therein. This method may be practiced by inserting a texturizing step at some point in time before the kiss-buffing step (4) in the protocol set forth above. Alternatively, a fully processed texturized disk, such as one originally produced for use with a flying head, may be retro-processed to within the topographic Specifications of the present invention by stripping the lubricant, kiss-buffing and relubricating the disk surface.
An interesting bonus benefit derived from the present invention, as we now see it, is that a medium (disk) prepared according to our teachings as these relate to texturized disks, results in a disk structure useable both in contact and in non-contact (flying) environments.
These and other features, objects and advantages that are offered by the structure and method of the present invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.